Add suggestion of similar macro names to macro undefined error message

Author: fhartwig

src/librustc/lib.rs

@@ -152,7 +152,6 @@ pub mod util {
     pub mod common;
     pub mod ppaux;
     pub mod nodemap;
-    pub mod lev_distance;
     pub mod num;
     pub mod fs;
 }

src/librustc_resolve/lib.rs

@@ -63,7 +63,6 @@ use rustc::middle::privacy::*;
 use rustc::middle::subst::{ParamSpace, FnSpace, TypeSpace};
 use rustc::middle::ty::{Freevar, FreevarMap, TraitMap, GlobMap};
 use rustc::util::nodemap::{NodeMap, DefIdSet, FnvHashMap};
-use rustc::util::lev_distance::lev_distance;
 
 use syntax::ast;
 use syntax::ast::{CRATE_NODE_ID, Ident, Name, NodeId, CrateNum, TyIs, TyI8, TyI16, TyI32, TyI64};
@@ -73,6 +72,7 @@ use syntax::ext::mtwt;
 use syntax::parse::token::{self, special_names, special_idents};
 use syntax::ptr::P;
 use syntax::codemap::{self, Span, Pos};
+use syntax::util::lev_distance::lev_distance;
 
 use rustc_front::intravisit::{self, FnKind, Visitor};
 use rustc_front::hir;

src/librustc_typeck/check/mod.rs

@@ -110,7 +110,6 @@ use TypeAndSubsts;
 use lint;
 use util::common::{block_query, ErrorReported, indenter, loop_query};
 use util::nodemap::{DefIdMap, FnvHashMap, NodeMap};
-use util::lev_distance::lev_distance;
 
 use std::cell::{Cell, Ref, RefCell};
 use std::collections::{HashSet};
@@ -123,6 +122,7 @@ use syntax::codemap::{self, Span, Spanned};
 use syntax::owned_slice::OwnedSlice;
 use syntax::parse::token::{self, InternedString};
 use syntax::ptr::P;
+use syntax::util::lev_distance::lev_distance;
 
 use rustc_front::intravisit::{self, Visitor};
 use rustc_front::hir;

src/libsyntax/ext/base.rs

@@ -24,6 +24,7 @@ use parse::token;
 use parse::token::{InternedString, intern, str_to_ident};
 use ptr::P;
 use util::small_vector::SmallVector;
+use util::lev_distance::lev_distance;
 use ext::mtwt;
 use fold::Folder;
 
@@ -776,6 +777,22 @@ impl<'a> ExtCtxt<'a> {
     pub fn name_of(&self, st: &str) -> ast::Name {
         token::intern(st)
     }
+
+    pub fn suggest_macro_name(&mut self, name: &str, span: Span) {
+        use std::cmp::max;
+
+        let mut min: Option<(Name, usize)> = None;
+        let max_dist = max(name.len() / 3, 1);
+        for macro_name in self.syntax_env.names.iter() {
+            let dist = lev_distance(name, &macro_name.as_str());
+            if dist <= max_dist && (min.is_none() || min.unwrap().1 > dist) {
+                min = Some((*macro_name, dist));
+            }
+        }
+        if let Some((suggestion, _)) = min {
+            self.span_help(span, &format!("did you mean `{}`?", suggestion));
+        }
+    }
 }
 
 /// Extract a string literal from the macro expanded version of `expr`,

src/libsyntax/ext/expand.rs

@@ -191,6 +191,7 @@ fn expand_mac_invoc<T, F, G>(mac: ast::Mac,
                 pth.span,
                 &format!("macro undefined: '{}!'",
                         &extname));
+            fld.cx.suggest_macro_name(&extname.as_str(), pth.span);
 
             // let compilation continue
             None

src/libsyntax/lib.rs

@@ -65,6 +65,7 @@ macro_rules! panictry {
 
 pub mod util {
     pub mod interner;
+    pub mod lev_distance;
     pub mod node_count;
     pub mod parser;
     #[cfg(test)]